Method and system for controlling a propulsion system of an alternatively powered vehicle

1. Field of the Invention

The invention relates to methods and systems for controlling propulsion systems of alternatively powered vehicles.

2. Background Art

Various methods are used to detect operating states of vehicle systems. U.S. Pat. No. 6,009,362 to Furukawa is an example of such a method. According to Furukawa, an anomalous condition detecting apparatus includes a detector for detecting a pair of positive and negative terminals of a fan motor. The apparatus also includes a decision circuit for deciding whether an anomalous condition exists based on a voltage detected between the terminals. An external resistor is provided between the positive terminal of the motor and a power source. The negative terminal of the motor is earthed. A voltage between the terminals is detected. The decision circuit decides that an anomalous condition exists when the potential of the positive terminal is smaller than a predetermined value.

U.S. Pat. No. 6,377,880 to Kato et al. is another example of such a method. According to Kato et al., a cooling fan failure detection apparatus for a hybrid vehicle comprises a cooling capacity calculation device, which calculates a cooling capacity of a cooling fan, a battery heating value calculation device, which calculates a heating value of a battery, and an assumed temperature change calculating device, which calculates an assumed temperature change of the battery based on the heating value and the cooling capacity. The apparatus further comprises an actual temperature change calculating device, which calculates an actual temperature change of the battery, and a failure determination device. The failure determination device determines whether the cooling fan is failing by comparing the assumed temperature change and the actual temperature change.

International Pub. No. WO 2006/095929 to Yanagida is yet another example of such a method. According to Yanagida, a start control repeatedly performs a start-up process for a start of an oil pump. In the event of a failed start-up of the oil pump by repetition of the start-up process, the start control specifies the occurrence of an abnormality in the oil pump or in the power supply to the oil pump at an outside air temperature that is not lower than a present reference temperature.

A propulsion system for and method for controlling an alternatively powered vehicle is provided. The propulsion system includes an electric machine having a maximum output torque, power electronics to control the electric machine and a coolant to cool the electric machine and power electronics. An expected temperature difference between the coolant and the power electronics is determined. An actual temperature difference between the coolant and the power electronics is also determined. Whether the actual temperature difference is greater than the expected temperature difference is determined and the maximum output torque of the electric machine is reduced if the actual temperature difference is greater than the expected temperature difference.